1. Field of the Invention
The present invention relates to an electroluminescent element (or device) adapted for use in a flat light source, a flat display, or the like. In particular, the present invention relates to a light emitting element utilizing a polymer compound as a light emitting material, and, more specifically, it relates to a light emitting element with improved stability and light emitting efficiency by employing a polymer compound having a metal bond as a light emitting material.
2. Related Background Art
Of the electroluminescent elements, an element utilizing an organic substance as a light emitting material is called an organic electroluminescent element or an organic EL element. Such an organic EL element is being actively developed for realization of the element, including material development therefor, since it has advantages of easier increase of size, light emission of a desired color by the development of various new materials and drive with a lower voltage in comparison with an inorganic EL element, and is promising as a light emitting element of a high-speed response and a high light emitting efficiency.
In the following description, following abbreviations will be used for various materials which have following names and structures shown in the following chemical formula I:    Alq3: aluminum-quinolinol complex;    α-NPD: N4,N4′-di-naphthalen-1-yl-N4,N4′-diphenyl-biphenyl-4,4′-diamine;    CBP: 4,4′-N,N′-dicarbazole-biphenyl;    BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline;    PtOEP: platinum-octaethylporphyrin complex;    Ir(ppy)3: iridium-phenylpyridine complex;

Currently, in order to increase the light emission luminance of the organic EL element, there is required development of a novel light emitting material for the organic EL element. From such a standpoint, attention is being paid, in addition to the conventional fluorescent light emitting materials, to phosphorescent light emitting materials for which a high light emitting efficiency can be expected in principle.
Also, there have been proposed those light emitting substances which are formed by incorporating a metal complex capable of emitting light upon application of an electric field or the like into a polymer material.
The present invention is characterized by employing a polymer compound containing a metal complex as a light emitting substance. Hitherto, as a polymer compound containing a metal complex, there have been known light emitting polymer materials disclosed in the following document 1.
Document 1: Photophysics of metal-organic π-conjugated polymers, K. D. Ley et al., Coordination Chemistry Reviews, 171 (1998), pp. 287–307
Document 1 reports measurement of photoluminiscence using the following compound and also suggests application to an organic EL element.

In the organic EL element of a low molecular type which is now in the main stream of the development, a light emitting material is formed on a substrate by vacuum evaporation. However, if such a polymer compound is made available, it will become possible to produce an organic EL element by a coating method, thereby leading to a significant cost reduction.
However, based on the experience of the present inventors, the compound described in the aforementioned Document 1 is estimated to lack stability because of instability of the C═O bonds contained in the Re complex. Also it is estimated to lack photostability because a triple bond is contained in the main chain of the polymer compound.
On the other hand, a report on O-17 by C. L. Lee et al. in the following document 2 discloses synthesizing a polymer compound having a phenylpyridine group on a side chain and then adding a metal complex thereto to synthesize a polymer compound having a metal complex in the side chain.
Document 2: C. L. Lee et al., “Polymer electrophotoluminescent devices using a copolymer of Ir(ppy)2-bound2-(4-vinylphenyl)pyridine with N-vinylcarbazole”; 3rd International Conference on Electro-luminescence of Molecular materials and Related Phenomena (Sep. 5th–8th, 2001).
However, it is estimated to be difficult to prepare a desired polymer by this technique, because a proportion of adding the complex (called introduction rate) is difficult to control and it is difficult to simultaneously introduce metal complexes of plural kinds into a polymer.
In consideration of the foregoing, it is, therefore, an object of the present invention to provide a polymer compound, having a high stability and containing a metal complex as a light emitting substance, with a high reproducibility and a high yield.
It is another object of the present invention to incorporate a light emitting metal complex with an arbitrary structure into a polymer compound, thereby obtaining a predetermined structure with an improved light emitting efficiency and also obtaining a predetermined color of light emission.